Pressure indicating devices

ABSTRACT

A pressure indicating device, e.g. for securing to a tire valve, is disclosed. The device includes a flexible impermeable diaphragm on one wall of a permanently hermetically sealed chamber is pressurized to a given pressure. A mechanical linkage moves depending on whether the pressure, e.g. in a tire to which the device is attached, is greater or less than that in the chamber, e.g., rotates a bicolored ball so that the color displayed provides a visual signal that indicates if the tire pressure is above or below the given pressure. This enables a puncture or air loss to be detected by a rapid glance.

This invention relates to pressure indicating devices and particularlybut not exclusively to such devices for indicating vehicle tyrepressure.

A wide variety of pressure indicating devices have been known for sometime, the majority being devices which provide a means to accuratelymeasure pressure, particularly of gases and liquids.

In certain situations, a precise measurement of pressure is not requiredbut rather a simple and clear indication of a change in pressure isdesired, for example to detect leakage from a pressurised container. Insuch situations, a device which provides a highly visual“see-at-a-glance” indication that leakage is occurring is moreappropriate than a precise numerical measurement of the pressure withinthe container.

Such devices are well known in the art. For example, a device is knownfor indicating whether a pneumatic circuit is pressurised, availableunder the trade mark ROTOWINK (ex Norgren Martonair Limited). Thisdevice is adapted to be mounted on a control panel, with the inletconnected to part of a pneumatic circuit, e.g. a pressure vessel, suchas a compressor reservoir. The device contains a flexible, impermeablediaphragm that spans the inlet. The diaphragm supports a springreturnable piston.

A rod and crank arrangement extends from the piston, terminating in thehead of the device, remote from the inlet, where the rod is attached toa crank within a rotatable ball having its opposite halves differentcolours, e.g. red and green. The ball is mounted beneath a lens throughwhich one side of the ball is clearly visible from the exterior of thedevice.

A difference in pressure across the diaphragm, e.g. resulting from abuild up of air pressure in a compression chamber to which the inlet ofthe device is connected, causes the diaphragm to flex towards the headof the device, which pushes the piston and rod towards the head. Thismovement causes the crank to cause the ball to rotate such that theother side of the ball is then visible through the lens. This other ballside of contrasting colour provides a clear visual signal that pressurehas built up in the chamber.

It is highly desirable for vehicle tyres to remain at their optimumpressure for reasons of safety, fuel economy and comfort and to prolongthe life of the tyres. Consequently, it is preferable that tyrepressures are checked at regular intervals. However, this mundane taskis frequently overlooked since a lower than optimal tyre pressure, suchas caused by a slow puncture or an inaccurate gauge on a pump orcompressed air supply unit, is only perceived when the tyre looksdangerously flat and/or the vehicle feels uncomfortable, at which stagethe tyre pressure is well below its optimum. Clearly, in the periodbetween initial loss of air pressure and detection, any use of thevehicle reduces the life of the tyre significantly and will have put thedriver and passengers of the vehicle at some risk.

Although it occurs less often, it is also potentially dangerous to drivea vehicle with one or more of its tyres grossly over inflated ratherthan under inflated.

Attempts have been made in the past to provide tyre pressure monitoringdevices. U.S. Pat. No. 4,814,745 describes a cap for attachment to atyre valve following inflation and which includes an alarm circuit whichis de-energised when the tyre is inflated to proper pressure. The cap,however, must include its own power supply and other circuit memberswhich is undesirably complex, prone to failure and expensive.

U.S. Pat. No. 4,819,686 discloses a purely mechanical device including adiaphragm in a chamber. The diaphragm may be deflected to give a visualindication of the state of pressure within the tyre. One side of thediaphragm is a so-called reference chamber which, when the device isapplied to a tyre valve stem, is pressurised to the pressure within thetyre. Thereafter the reference chamber is sealed while the other side ofthe diaphragm is exposed to the pressure within the tyre, so that if thelatter drops, the diaphragm moves. The construction is relativelycomplex and the cap provides no indication as to whether the tyre isinflated to the correct pressure. The device is only effective to show adrop in pressure over time. British patent specification 2277802discloses a similar device but in which an indication of the state ofpressure in the tyre is achieved only with the use of a hand held deviceadapted to be brought into close proximity with the cap on the valvestem. It suffers from the same disadvantage as noted above.

U.S. Pat. No. 2,689,481 describes a tyre pressure indicating devicecomprising a housing which may be screwed on to a tyre valve stem andwhich includes an inlet for air under pressure from the tyre into atransparent walled chamber. The chamber contains a hermetically sealedbellows, the degree of compression of which changes its length toprovide, in conjunction with markings on the exterior of the chamber, anindication of tyre pressure.

According to the present invention there is provided a pressureindicating device comprising a housing which includes an inlet for airunder pressure, a permanently hermetically sealed chamber including agas under pressure, a flexible member between the inlet and the chamber,and a signalling device, the signal from which depends on the pressuredifference between the inlet and the chamber, and characterised in thatthe flexible member is a flexible impermeable diaphragm which, as thepressure at the inlet increases, is caused to flex to extend into thepressurised chamber, and in that the device includes connecting meansbetween the diaphragm and the signalling device adapted to actuate thesignalling device to provide a signal representative of the inletpressure relative to that in the sealed chamber. The signalling deviceis preferably located within the sealed chamber.

When such a device is to be used as a tyre pressure indicating device,the inlet may be adapted to form sealed contact with the valve when thedevice is fitted to the tyre valve stem in place of the conventionaldustcap and, as it is screwed further on, to open the tyre valve so thatthe pressure in the inlet is the same as that in the tyre.

Preferably the chamber is pressurised to a pressure just below that ofthe optical tyre pressure for a particular vehicle, (the optimal tyrepressures being taken to be those recommended by the vehiclemanufacturers). Consequently, when the device is connected to and opensthe valve, the pressure differential between the higher pressure of thetyre and the lower pressure of the chamber causes the flexibleimpermeable diaphragm to flex, such that it extends into the pressurisedchamber, and to actuate the signalling device to provide a signalrepresentative of the tyre pressure relative to that in the sealedchamber.

The diaphragm construction may be a flat disc type or (and this mayimprove service life and sensitivity of the diaphragm) a rollingdiaphragm.

Preferably the signalling device is capable of providing at least twovisually distinguishable signals. This is most conveniently achieved bya mechanical means such as a rotatable mounted ball of which one side isone colour and the other a contrasting colour but as will beappreciated, any mechanical means of providing such signals may besubstituted. The signal is preferably clearly visible over a wide rangeof viewing angles, e.g. a viewing angle of 110° or more.

The means connecting the flexible impermeable diaphragm to thesignalling device are preferably simple mechanical linkages capable oftransmitting any movement of the diaphragm, in a manner which actuatesthe signalling device. Most preferably a spring returnable pistoncarrying an elongate member is mounted on the diaphragm, the end of themember being pivoted to a crank which is attached to a rotatable ballsignalling device. In use, any flexing or flattening of the diaphragmwill accordingly rotate the ball in one sense or the other.

In accordance with a particular preferred feature of the invention, thediaphragm may have a weakened section adapted to rupture if the pressurein the tyre exceeds that in the chamber by a predetermined amount. Ifsuch a diaphragm is used, when the device is fitted to an over inflatedtyre, the indicator will briefly indicate adequate tyre pressure andthen on rupture of the diaphragm, that all is not well.

The inlet of the device preferably has a screw threaded bore and at theend of the bore an axial nose which is positioned to depress the centralpin of and therefore open, a conventional tyre valve. To ensure that thevalve and device are in sealed contact and to prevent the escape of airfrom within the tyre, the inlet preferably contains an appropriatelylocated O-ring.

A tyre pressure indicating device according to the present invention maythus easily be fitted onto any conventional tyre valve to display aclear visual signal which indicates the air pressure condition of thetyre. It may be mass produced inexpensively in quantity. It is alsolightweight, self-contained and provides an indication of self-failure.

A device according to the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic vertical section through a tyre pressureindicating device according to the invention, wherein the diaphragm isin the fully flexed position,

FIG. 2 is the device of FIG. 1 wherein the diaphragm is in the positiontaken when the inlet is not mounted on a tyre valve.

With reference to FIG. 1, a low tyre pressure warning device 2, having agenerally cylindrical casing 9, is mounted onto a vehicle tyre valve byscrew-threading on to the valve housing 1. A nose 6 at the end of athreaded bore 4 in the casing of device 2 depresses the central pin 21of the valve. An O-ring 5 ensures a sealed contact between the deviceand the valve housing 1. Depressing pin 21 allows pressurised air fromthe tyre to enter, via inclined ports 3, the space between the nose 6and a flexible impermeable diaphragm 7 sealed to the casing 9.

The flexible diaphragm 7 spans the inlet and is held in position by aflange 11 on the inner wall of casing 9. It has a weekened region 18which will rupture if the pressure in the inlet exceeds that in chamber8 by more than a predetermined amount.

Within casing 9, a chamber 8 above the diaphragm 7 as shown in thedrawings is pressurised and is completely permanently hermeticallysealed during manufacture of the device. This chamber 8 contains apiston 10 urged by a compression spring 13 towards diaphragm 7. Spring13 seats on an annular bead 24 in casing 9. A piston rod 12 extendsupwardly and is pivoted to a shaft 20 not quite running through thecentre of a dual colour ball 14. Ball 14 has on its exterior two smallpins defining an axis of rotation 22, and which are seated in twocorresponding formations in the inner wall of casing 9, so mounting ball14 rotatably about axis 22 within the casing. The ball 14 is visiblefrom the exterior of the device through a transparent lens region 16 ofthe casing 9. One half is denoted G and is green in colour, the otherhalf, denoted R, being red. Rod 12 passes through an arcuate slot in theball. Piston 10 has a perforation bore 17 to ensure that the pressure isequal on each side of the piston.

The chamber 8 is hermetically sealed during manufacture at a pressurehigher than atmospheric but slightly lower than the optimal pressure ofthe tyre to which the device is to be secured. Therefore, when the tyrepressure is optimum, the higher pressure behind the diaphragm 7 causesit to flex to the position shown in FIG 1. This movement of thediaphragm, when the device is threaded on to the tyre valve, causes thepiston 10 and rod 12 to rise to the position as shown in FIG. 1 andaccordingly to rotate the ball 14 so that its green half G is visiblethrough the transparent lens 16. This provides a clear visual signalwhich indicates that the pressure in the tyre is sufficiently above thepressure in chamber 8 to overcome the force exerted by spring 13.

However, if, for example, a tyre to which the device is attacheddevelops a slow puncture, the tyre pressure reduces. This reduction inpressure behind the flexible diaphragm 7 causes it to flatten as thepressure of the tyre and of the sealed chamber equalize. When thepressures are approximately equal, the flexible diaphragm 7 is flat andthe piston 10 and rod 12 consequently drop under the influence of spring13, to the position shown in FIG. 2.

This downward movement causes ball 14 to rotate so that the red half Ris now visible through the transparent lens 16, accordingly providing aclear visual signal which indicates that the tyre pressure has reduced.

As will be appreciated, the ball may bear further colours in order toindicate an intermediate stage between the fully flexed position andfully flattened position of the diaphragm.

The device of the invention enables the easy detection of a slowpuncture, or the like, in a vehicle tyre before it would usually beperceived from observation of the tyre alone, especially with modern“low-profile” tyres. The device may easily be produced in a range of“changeover” pressures to match the range of recommended tyre pressuresacross a wide range of motor vehicles. If desired, two sets of suchdevices may be provided as standard, one for use when the vehicle isunladen or only lightly loaded, the other for use when the vehicle isladen where slightly higher tyre pressures are often recommended.

It should be noted that the device of the invention, if it is itselfsubject to failure, e.g. by rupture of diaphragm 7, immediatelyindicates such failure to the user; when, after pressurising the tyre tothe correct pressure, the device is fitted on to the tyre valve stem,the chamber 8 pressure rises to equal the tyre pressure but, because ofspring 13, the mechanical linkage does not move, so the tyre stillappears under-pressurised. Failure of the ball to turn when the deviceis fitted back on is immediately apparent.

Likewise, if the seal ring 5 should fail, or the casing crack adjacentthe seal ring by being screwed on too tightly, then the pressure in thetyre will drop and the indicator will turn red.

If the seal of chamber 8 should fail, the substantial pressuredifferential will rupture diaphragm 7 at region 18 which thus acts as abursting diaphragm. It will also rupture if the pressure in the inletexceeds the pressure in the chamber 8 by more than a given thresholde.g. if the pressure in the tyre is greater than twice the pressure inthe chamber 8. The device will thus fail if the tyre onto which it isscrewed is subject to gross over-pressure, thus giving a very positiveindication to the user, when the device is screwed onto the valve stem,that something is seriously wrong.

In an alternative approach to providing a weakened region 18, loss ofpressure in chamber 8, or gross tyre over-pressure, can cause the stem12 to buckle and e.g. release something in the chamber which will causethe window to adopt a different appearance.

The foregoing specific description of a preferred embodiment and thegenerality of the description of the invention have been directed to theuse of the device in connection with tyres but the device is notrestricted to such use. Thus it may be used in analogous situationswhere it is desired to monitor any drop in pressure below a presetdesired figure, for example to monitor the condition of pressurised fireextinguishers, to monitor bladder pressure in hydraulic accumulators andfor monitoring the integrity of closed tubes. In this last application,a closed tube e.g. in a mechanical or civil engineering structure, hasits interior pressurised to a given value and a device in accordancewith the invention then attached. If a crack appears in the tube or e.g.at a weld at one end of the tube, the pressure within the tube will dropand this can be immediately perceived by looking at the device of thepresent invention attached thereto.

What is claimed is:
 1. A pressure indicating device comprising a housingwhich includes an inlet for air under pressure; a permanentlyhermetically sealed chamber sealed during manufacture of the device,said chamber containing a gas under pressure; a signaling deviceconstructed and arranged to provide a signal that depends on pressuredifference between the inlet and the chamber; a flexible impermeablediaphragm separating the inlet and the chamber, the diaphragmconstructed and arranged to flex and extend into the chamber as pressureat the inlet increases; and a connecting means between the diaphragm andthe signaling device to actuate the signaling device to provide a signalindicative of inlet pressure relative to pressure of the sealed chamber.2. The pressure indicating device of claim 1, wherein the signalingdevice is located within the chamber.
 3. The pressure indicating deviceof claim 1, wherein the inlet is adapted to open a tire valve and form asealed contact with said tire valve.
 4. The pressure indicating deviceof claim 3, wherein the chamber is pressurized to a pressure just belowthat of an optimal tire pressure for a particular vehicle and vehicleload condition.
 5. The pressure indicating device of claim 1 or 2,wherein the inlet includes a nose adapted to depress a central pin of avalve as the device is attached to the valve.
 6. The pressure indicatingdevice of claim 5, wherein the inlet comprises a seal adapted to sealthe device to the valve.
 7. The pressure indicating device of claim 1,2, 3 or 4, wherein the signaling device is capable of providing at leasttwo distinguishable signals.
 8. The pressure indicating device of claim7, wherein the signaling device is mechanical.
 9. The pressureindicating device of claim 8, wherein the signaling device comprises arotatably mounted ball having at least two colored regions.
 10. Thepressure indicating device of claim 1, wherein the device is a visualindicator that is perceptible over a viewing angle of at least 110°. 11.The pressure indicating device of claim 1, wherein the connecting meanscomprises mechanical linkages.
 12. The pressure indicating device ofclaim 11, wherein the connecting means comprises an arrangement of apiston, an elongate member and a crank means, and wherein the piston ismounted to lie against the diaphragm, the crank means is attached to thesignaling device, and the elongate member extends between the piston andthe crank means.
 13. The pressure indicating device of claim 12, whereinthe piston is spring biased toward the diaphragm.
 14. The pressureindicating device of claim 1, wherein the diaphragm is constructed as orincorporates a bursting disc.
 15. The pressure indicating device ofclaim 14, wherein the bursting disc is constructed and arranged torupture when applied pressure on a side of the diaphragm remote from thechamber exceeds twice the pressure in the chamber.